1. Field of the Invention
The present invention relates to a rotor for machines such as centrifugal machines, and in particular, to the rotor of which swinging functions of buckets are surely prevented from being slid.
2. Related Art
There are various kinds of swing rotor for centrifugal machines. Of these, a conventional swing rotor generally includes buckets, into which a specimen is put, and cylindrical rotor pins each serving as a fulcrum for the bucket. Each rotor pin is attached to each side of each bucket and connected to each arm of the rotor, so that the bucket can be swung about the rotor pin.
The rotor pins are arranged in parallel to the center axis for swinging of the bucket, and in many cases, fixed to either the rotor or the bucket. The rotation of the rotor generates a centrifugal force that permits each bucket to swing with its bottom gradually shifted outward and lifted. At a pin-supporting portion of each bucket, there occur sliding motions between the rotor pin and the inner wall of the pin-supporting portion when the bucket swings. Therefore, in order to ensure that the swing motion is carried out with precision and stability, a lubricant or other anti-sliding materials must be applied to the portion at shorter and regular intervals.
The number of buckets is mostly even, and in most cases, 4 or less. When both sides of the bucket are supported by the rotor pins, a lateral hole must be bored into both sides of each arm part of the rotor, so that the bucket can be attached to the rotor. However, the number of buckets is large (for example, 6 or more), a bucket-arrangement angle relatively made to a certain adjacent bucket becomes smaller, so the space between the two mutually adjacent buckets is narrowed. Accordingly, a lateral boring work to the sides of the arm becomes difficult, limiting the choices of how to attach the rotor pin.
To overcome such a situation, one measure is that the rotor pin is attached to the bucket to be supported by each arm of the rotor. Another measure is illustrated in FIG. 1, in which reference numerals 5, 6 and 7 show a bucket, a pin portion attached to a rotor body, and an arm extended from the rotor body, respectively. In this configuration, the pin portions 6 are integrally formed with the arms 7 by means of casting or the like. Each bucket 5 is hooked up at both the pin portions 6 each projected inward from given upper parts of each arm 7. For the sake of an easier understanding. FIG. 1 is drawn with one bucket 5 omitted
Alternatively, for only a narrow spacing is left between adjacent two buckets, adjacent two rotor pins are made integrally as one pin and both tips of the integral pin are bent at a certain angle that agrees with an angle between the pin""s axial direction and a swinging axis direction. Such pin is fixed in place to each arm, so that the buckets can be swung.
As mentioned above, in the conventional swing rotor, there occur sliding motions in the contact between the rotor pin and the pin-supporting portion of the bucket. Though the bucket should return to its original standing-up position when the rotor stops rotating, there are some cases in which the bucket stops by friction before it returns to the original standing-up position. Especially, in the case of an automatic centrifugal machine that automatically charges and discharges a specimen into and from the bucket, such incomplete return of the bucket to the its original position will lead to various serious situations. For example, no specimen will be automatically discharged from the bucket if such incomplete return really happens. What is worse, a stop of the rotor and/or damages of a specimen and the machine may be caused. To avoid such undesired situations requires that grease or other materials for lubrication be applied frequently to the pin-supporting portions. However, there is an inconvenience that this application needs much work.
An object of the present invention is to solve the above problems, that is, to maintain a simplified structure of the rotor in which a large number of buckets are arranged, while eliminating incomplete swinging motions of the buckets and to reduce the number of times of regular maintenance, thereby improving reliability of a machine in which a specimen is automatically charged and discharged into and from the buckets.
In order to accomplish the above object, the present invention is basically provided by a rotor used for a centrifugal machine and the rotor comprises a rotor body, a plurality of buckets, and a plurality of rotor pins. The rotor body is driven to rotate, the rotor body having a plurality of arms around the rotor body. A hole is formed in place in each arm. The plurality of buckets are arranged around the rotor body so as to be swingable between any two of the arms. The plurality of rotor pins are each inserted through each of the holes and arranged in a direction of a normal line to a rotation axis of the rotor body so as to swingably support any two of the buckets by both ends of each rotor pin. Each of both the ends is shaped into a tapered form having a predetermined taper angle and extending in diameter outwardly to an axis of the rotor pin.
Preferably, the taper angle given to each end of each rotor pin is at least substantially equal to an angle made between a swinging axis of each bucket and a center axis of each rotor pin. It is particularly preferred that the taper angle is substantially equal to the angle made between the swinging axis of each bucket and the center axis of each rotor pin.
Still preferably, any two of the buckets supported are mutually adjacent two buckets with any one of the arms located therebetween.
It is also preferred that each rotor pin is rotatable to each arm.
Further it is preferred that an accepting portion for each rotor pin formed in each bucket is a cylindrical hole of which diameter is larger than an outermost diameter of each tapered end of the rotor pin.
Thus, during the rotation of the rotor body that causes a centrifugal force, each tapered end of the rotor pin is brought into contact with the inner wall of the hole of each bucket under a line contact. This line contact makes swinging motions of the buckets smooth, thus avoiding an incomplete return of each bucket to its original standing-up position. The smooth and stable swinging motions of the buckets eliminate the necessity of applying grease to the rotor pins so often. Any particular parts are not added to the rotor, so the simplified construction of the rotor is still maintained.